Bottled water may be a waste because water is pretty indistinguishable from its competitors outside of visual design of the product container, but not everything is so generic. I bought a bag of granola the other day that had a QR code on the back that I thought worked well.

As I idly sat at my breakfast table last week, I was reading the back of the bag and thought "this stuff is pretty damn good, I wonder what their QR code does?" I scanned it and was sent to their site where they displayed their entire product line, leading me to discover a different variety of their product I wanted to try (and have since purchased). Since I was groggy and not feeling very interactive at 6am, the bag of granola probably couldn't have convinced me to type in a URL into my phone no matter how tasty their product was, so I'd say their QR code worked (typing URLs is comparatively a lot of work compared to two taps of my phone to scan QRs)

As a product discovery mechanism I think they're probably ok, especially for existing customers that may like your brand but may not know everything about you. I don't think they'd be great on billboards or television ads, but as part of a product label design, I think it's a great way to provide more information to the consumer than would otherwise fit in that space.